1. Field of the Invention
The present invention relates to an apparatus for extruding a ceramic molding having a honeycomb structure, etc.
2. Description of the Related Art
In recent years, a ceramic molding having a honeycomb structure comprised of a plurality of cells divided by partitions has been used as a catalyst carrier for treating the exhaust gas of an automobile.
To manufacture a ceramic molding with a honeycomb structure, an extrusion molding is generally performed by using a plunger or screw type of extruding apparatus.
Especially, the screw type extruding apparatus provided with an extrusion screw to knead and extrude a ceramic material into a molding die can successively produce ceramic moldings of honeycomb structure with high productivity.
However, the above conventional screw type extruding apparatus has the following problems. In the screw type extruding apparatus, the outer diameter of the ceramic molding which can be extruded is restricted in accordance with the diameter of the extrusion screw. It is difficult to extrude the ceramic molding of which the ratio of the outer diameter thereof to the screw diameter exceeds a predetermined value. In order to extrude a ceramic molding having such a large outer diameter, it is necessary to use a large extruding apparatus provided with an extrusion screw having a large diameter.
Especially, to extrude a ceramic molding having a honeycomb structure in which the cells are divided by thin partitions, it is preferable that the diameter of the ceramic molding be restricted to be approximately 0.7–0.8 times the screw diameter of the extrusion screw.
To extrude the ceramic molding mentioned above, the ceramic material must be uniformly distributed over the entire section of the ceramic molding. To this end, a resistance pipe whose diameter is reduced toward the molding die must be provided between an outlet side of the extrusion screw and the molding die. The resistance pipe can enhance the uniformity of the ceramic material due to a friction resistance generated between its inner peripheral wall and the ceramic material.
To maintain the pressure necessary for extrusion molding in the extrusion screw, the screw length must be increased in accordance with the screw diameter. That is, to manufacture a ceramic molding having a large diameter, a long extrusion screw having a large diameter is required. This is the reason that it is difficult to manufacture a ceramic molding having a large diameter using a small extruding apparatus.